1. Field of the Invention
In general, the present invention relates to counterbalance systems for windows that prevent open window sashes from closing under the force of their own weight. More particularly, the present invention system relates to counterbalance systems for tilt-in windows that use curl springs to create a counterbalancing force.
2. Description of the Prior Art
There are many types and styles of windows. One of the most common types of window is the double-hung window. A double-hung window is the most common window found in traditional home construction. A double-hung window consists of an upper window sash and a lower window sash. Either the upper window sash or the lower window sash can be selectively opened and closed by a person sliding the sash up and down within the window frame.
A popular variation of the double-hung window is the tilt-in double-hung window. Tilt-in double-hung windows have sashes that can be selectively moved up and down. Additionally, the sashes can also be selectively tilted into the home so that the exterior of the sashes can be cleaned from within the home.
The sash of a double-hung window has a weight that depends upon the materials used to make that window sash and the size of the window sash. Since the sashes of a double-hung window are free to move up and down in the frame of a window, some counterbalancing system must be used to prevent the window sashes from always moving to the bottom of the window frame under the force of their own weight.
For many years counterbalance weights were hung next to the window frame in weight wells. The weights were attached to the window sash using a string or chain that passed over a pulley at the top of the window frame. The weights counterbalanced the weight of the window sashes. As such, when the sashes were moved in the window frame, they had a neutral weight and friction would hold them in place.
The use of weight wells, however, prevents insulation from being packed tightly around a window frame. Furthermore, the use of counterbalance weights on chains or strings cannot be adapted well to tilt-in double-hung windows. Accordingly, as tilt-in windows were being developed, alternative counterbalance systems were developed that were contained within the confines of the window frame and did not interfere with the tilt action of the tilt-in windows.
Modern tilt-in double-hung windows are primarily manufactured in one of two ways. There are vinyl frame windows and wooden frame windows. In the window manufacturing industry, different types of counterbalance systems are traditionally used for vinyl frame windows and for wooden frame windows. The present invention is mainly concerned with the structure of vinyl framed windows. As such, the prior art concerning vinyl framed windows is herein addressed.
Vinyl framed, tilt-in, double-hung windows are typically manufactured with tracks along the inside of the window frame. Brake shoe mechanisms, commonly known as “shoes” in the window industry, are placed in the tracks and ride up and down within the tracks. Each sash of the window has two tilt pins or tilt posts that extend into the shoes and cause the shoes to ride up and down in the tracks as the window sashes are opened or closed.
The shoes serve two purposes. First, the shoes contain a brake mechanism that is activated by the tilt post of the window sash when the window sash is tilted inwardly away from the window frame. The shoe therefore locks the tilt post in place and prevents the base of the sash from moving up or down in the window frame once the sash is tilted open. Second, the shoes support curl springs. Curl springs are constant force coil springs that supply a constant retraction force when unwound. Traditionally, curl springs are placed within the shoe in the same way a metal tape is placed within the housing of a tape measure. One end of the curl spring is anchored to the frame of the window while the main body of the curl spring is wound inside of the shoe. As the shoes move within the tracks, the curl spring rotates inside the shoe. Often as the curl spring rotates inside the shoe, the curl spring moves around within the confines of the shoe and makes an undesirable noise.
Single curl springs are used on windows with light sashes. Multiple curl springs are used on windows with heavy sashes. The curl springs provide the counterbalance force to the window sashes needed to maintain the sashes in place. The counterbalance force of the curl springs is transferred to the window sashes through the structure of the shoes and the tilt posts that extend from the window sash into the shoes.
Prior art shoes that contain braking mechanisms and support counterbalance curl springs are exemplified by U.S. Pat. No. 6,378,169 to Batten, entitled Mounting Arrangement For Constant Force Spring Balance; U.S. Pat. No. 5,463,793 to Westfall, entitled Sash Shoe System For Curl Spring Window Balance; and U.S. Pat. No. 5,353,548 to Westfall, entitled Curl Spring Shoe Based Window Balance System.
Prior art shoes for curl spring counterbalance systems are complex assemblies. The shoes must contain a brake mechanism strong enough to lock a sash in place. Furthermore, the shoes must engage and retain the end of at least one strong curl spring. Prior art shoes are always in contact with the tracks on the sides of the window frame. Accordingly, as wear, dirt and grime accumulate over time, it often becomes more difficult for the shoes to move up and down. The shoe of a window assembly therefore often malfunctions.
If a shoe jams or otherwise malfunctions, the shoe may not enable the tilt post of the window sash to rotate freely as the window sash is tilted inward. As a window sash is tilted inward, a large torque is experienced by the tilt post at the base of the window sash. This torque is used to activate the braking mechanism in the shoe. However, if the shoe jams, slides out of its track, or otherwise malfunctions, the shoe may not allow the tilt post of the window sash to rotate freely. Consequently, the large torque force, created by the window sash being tilted, acts upon the tilt post at the bottom of the window sash. If the tilt post is not free to rotate, the torque force often bends the tilt post or breaks the tilt post off the sash. Once the tilt post is so damaged, it must be replaced. In many models of windows, the tilt post is manufactured as part of the sash structure and cannot be replaced. In such a construction, the entire window sash must be replaced if the tilt post becomes damaged.
Furthermore, the manufacturing process used to create a window sash with an integral tilt post is complex. As such, the cost of manufacturing such a window sash is far greater than it would be if no tilt post were present.
A need therefore exists in the field of vinyl, tilt-in, double-hung windows, for a counterbalance system that eliminates the need for shoes. A need also exists in the field of vinyl, tilt-in double-hung windows for a counterbalance system that provides inexpensive, easily installed tilt posts for a window sash. As such, window assemblies can be made more reliable, less noisy, less expensive and easier to repair. These needs are met by the present invention as described and claimed below.